The invention relates to an X-ray system and an ultrasound system which generate images or sequences of images and modify or optimize the operational behavior of individual system components. The invention also relates to a method of controlling such system components.
During a medical X-ray examination by means of a series of X-ray images, the physician is often confronted with the problem of having to adjust, in addition to carrying out the actual examination, also the operational behavior of individual components of the X-ray examination system in order to achieve an optimum quality of the X-ray images in the image regions of interest. Optimum adjustment of the X-rays is of particular importance. On the one hand, an increase of the radiation dose usually enhances the image quality, but on the other hand the object to be examined should be exposed to an as small as possible radiation dose only. The requirements imposed on the image quality as a result thereof are normally defined by the type of examination while minimizing at the same time the radiation dose for the object to be examined. Various possibilities are known for automatic control of the X-ray dose by the system. To this end, during operation the system usually extracts information from images or image regions in order to readjust the dose automatically on the basis thereof. When the X-ray dose is controlled on the basis of the complete image contents, such control often leads to unsatisfactory results because the control is adversely affected by changing image regions and image regions which are strongly overexposed or underexposed because of properties that are inherent of the system. Therefore, for example, the documents EP 0435528 and EP 0748148 disclose X-ray systems which extract information for dose control from predetermined image regions, that is, so-called regions of interest or ROI, instead of from the entire image.
These systems, however, have the drawback that the ROI is predetermined and hence static. This gives rise to the problem that the object region to be examined must be imaged in the image region of the ROI. If this is not the case, the dose will be controlled on the basis of incorrect image data. When a moving object is examined by means of series of images, the object is liable to leave the static ROI because of its motion, so that the dose control again operates on to basis of incorrect image data. In order to mitigate this problem, for example, the object or the system could be positioned anew, usually implying an unacceptable amount of additional work for the staff, or the ROI could be enlarged, be it at the expense of a degradation of control. For the adjustment of different system parameters it is necessary to use information from different ROIs.
The document JP 04002332 discloses an X-ray examination system for use during heart catheterizations; this system supports the physician in positioning a catheter on the basis of a rectangular image section which is taken from a larger image and which shows the tip of the catheter at the center and automatically follows the catheter during its motion. The selection and shifting of the rectangular section are carried out by means of a simple motion analysis in which two successive images are subtracted. Further aids, notably means for simplifying the operability of the system, are not made available to the physician. This system has the drawback that the images wherefrom the image section is taken must always be larger than the image section which contains the information of interest to the physician. Consequently, an unnecessarily large region of the patient is exposed to X-rays. Moreover, the image quality is not changed.